Patent GB-464027-A (GB)
Title: Improvements in or relating to apparatus for use in recording sound intensities
IPC: G01H3/12
Filed: 1935-10-04
Abstract: 464,027. Automatic voltage control systems. NEUMANN, G. Oct. 4, 1935, Nos. 27464, 27465, and 27466. Convention dates, Oct. 5, 1934, Nov. 8, 1934, and March 29, 1935. [Class 38 (iv)] [Also in Groups XXXVI and XXXVIII] In apparatus for recording sound intensities, the voltage variations from a microphone are amplified and applied to a logarithmically divided potentiometer, 3 the output from which is fed through an amplifier 5 to a valve 6 which supplies one energizing coil 10 of a clutch, the other coil 14 of which is supplied from a further valve 11 controlled by the voltage variations across the coil 10. The currents in the coils vary in opposite senses with variations of the input voltage of the potentiometer and the coils act differentially so as to magnetize a rotating disc 16 which attracts one or other of the prongs 18 or 19 of a fork so as to drive the movable contact 4 of the potentiometer to keep the output voltage of the potentiometer constant. A pointer 21 connected to the contact 4 is used to record the sound intensity. The anode of both the valves 6, 11 may be supplied from a common battery. In a modification, a single amplifying valve supplies both coils in series in its anode circuit and one of the coils is shunted by a circuit including a battery so that when full anode current flows in the valve the shunted coil carries no current but with decreasing anode current increasing flows through this coil. Alternatively, the amplifying valve may be of the double grid type with one of the coils in series in the anode circuit and the other in the circuit of the cathode screening grid. In a further modification, the signals are amplified and then rectified and the rectified currents control two separate amplifier valves supplying the two magnetizing coils. The bias potentials are so chosen that the currents in the anode circuits of the last two valves vary in opposite senses with variations in the input signal strength. Where it is desired to measure the ratio or quotient of two sound intensities, the logarithmically subdivided potentiometer P1, Fig. 9, supplied from one of them is controlled by apparatus H1 as above described and the pointer of the potentiometer P1 also operates on a potentiometer Pz supplied from the other sound detecting device. The output of the potentiometer Pz is then supplied through an amplifier V to a further potentiometer P2 which is controlled by a further automatic device H2 as above described and its pointer operates a recording pencil 5 to give a record of the ratio or quotient of the two sound intensities according to the sub-division of the potentiometers P1 and P2. Alternatively, the pointer G1 of the potentiometer P1 operates a rack and the pointer of a corresponding automatic potentiometer controlled from the other sound source operates a further rack, both the racks operating differentially on a pinion and arm carrying the recording stylus. In a further arrangement the pointer of one automatic potentiometer operates the recording stylus and the pointer of the other operates the paper strip or drum on which the record is made.